yamaha 40 hp 3 cylinder Autolube

[raczekp1]

Hi.
I'm working on yamaha 40 hp 3 cyl autolube, 3 carbs.
motor runs good on idle but when i thy to accelerate is not picking rpm, just bumping.
i can see good stream of fulel geting from 3 carbs to3 cylinders.
this model has timing advencer on cdi module.
advencer works (moving up and dowm) but looks like is noc accelerating.
tryed to disconect advencer arm from cdi.ors
moving advencer hook on cdi while trotle is on idle( carbs set on idle, not touched) motor starts geting rpm
but when i start moving carbs accelerating arm and secend hand advence a advencer on cdi motor start bumping without much rpm

 

[99yam40]

always give the complete model # so everyone knows what motor is being talked about.
you should know this by now.

Any way, it is easy to use a light to make sure timing is in spec and advancing as it should.
not sure what you are calling bumping

if it is what we call a lean sneeze, then I would say the main jets are plugging or water in bottom on fuel bowls

 

[raczekp1]

its not my motor but mine works almost hes same

https://www.youtube.com/watch?v=F6WsnWbn0XQ

 

[rejesterd]

If the issue only occurs when you quickly open the throttle, then check the acceleration pump. The service manual tells you how to perform this check.

Check the throttle linkage and synchronization of the throttle valves.

Check the carb needle valves for wear or debris.

Check the jets for clogs.

Test each spark plug wire with a spark tester to confirm good spark.

Warm up the engine, shut it down, then do a compression test on all cylinders.

If you find no issues up until this point, replace the spark plugs.